1. Technical Field of the Invention
The present invention relates to a polymerizable composition and an image-recording material using the polymerizable composition as a recording layer and, more particularly, to an image-recording medium which is writable by an infrared ray laser with high sensitivity and to a lithographic printing plate precursor.
2. Description of the Related Art
Recent years have seen a remarkable development of laser and, with respect to a solid laser and a semiconductor laser, those which have a large output and a small size have been developed. Therefore, these lasers are extremely useful as a recording light source in the direct plate-making based on digital signal, for example, from a computer.
As an image-recording medium using such laser as a recording light source, a thermally polymerizable recording layer has been known which contains a light-heat converting agent, a radical-generating thermal polymerization initiator and a thermally polymerizable resin. (see, for example, JP-A-8-108621).
A negative-working image-forming material having such thermally polymerizable recording layer usually utilizes a recording system wherein a polymerization is caused with a radical generated by light or heat to cure exposed areas which form image areas.
With such negative-working image-forming material, it is possible to improve properties such as reactivity and plate checkability by adding an ionic material or a highly polar compound as a dye or other constituent. However, such highly polar compound has a problem that, when stored under an atmosphere of high temperature, it can cause non-desired mutual action with a binder or a polymerizable compound to be used therewith and, as a result, that unexposed areas suffer reduction in dissolution rate in a developing solution, thus being liable to remain under ordinary developing conditions.
In the field of other image-recording materials than the thermally polymerizable image-recording material, for example, a positive-working image-recording material adapted for an infrared ray laser or a cross-linkable negative-working image-recording material containing an acid generator and an acid-crosslinking agent, a technique of using an alkali water-soluble dye has been proposed to reduce generation of remaining of unexposed areas or generation of dye stain upon alkali development (see, for example, JP-A-2000-267265). In such cases, however, application of the technique to a polymerizable composition has never been examined.